A grudge or grievence against a person or persons generated within a mosh pit.

Pit Beef is created mostly during hardcore/punk and/or metal shows, where moshing and dancing turns more into an angst driven argument or fight. Much like when dogs play with eachother and it appears as if they are fighting, so is the Mosh Pit. Encompassed within The Pit, sometimes moshing and dancing can generate Pit Beef with others, causing problems and kids "starting" with eachother.

Me and Brophy have Pit Beef. Last show he windmilled right into my sister.

I thought I had Pit Beef with that kid Potty, but then after the show he was buyin me beers.